Fullerenes referred to as C60 and C70, carbon clusters having a closed-shell structure, have been recently proposed as new carbon materials, for example, as shown in Japanese Patent No. 2802324. Since these materials are expected to show special properties because of their unique molecular structures, research on their properties and development of use has been increasingly made, and fullerenes are expected to be used in fields of, e.g., diamond coatings, battery materials, paints, heat insulating materials, antifrictions, pharmaceuticals, and cosmetics.
As a method for producing fullerenes, a method has been proposed in which a carbon compound is burned to produce fullerenes, for example, as shown in Published Japanese Translation of PCT International Application No. H06-507879. Also, another method has been proposed in which an aromatic hydrocarbon such as benzene and an oxygen-containing gas are introduced into a reactor and subjected to incomplete combustion under reduced pressure to produce fullerenes.
Fullerene-containing soot obtained by a combustion method etc. contains a fullerene mixture having any two or more of C60, C70 and higher fullerenes having greater than 70 carbon atoms (any one or more of C76, C78, C82, C84, C90, C96, C120, etc.), and a soot residue (e.g. polycyclic aromatic hydrocarbons such as acenaphthylene, fluorene, phenanthrene, pyrene, benzo[b]fluorene, benzo[c]phenanthrene, benzo[a]anthracene, triphenylene, and/or benzopyrene, carbon having a graphite structure, hydrocarbons having a graphite structure as a skeleton, and carbonaceous polymers such as carbon black). A solvent extraction method has also been known in which the soot is brought into contact with a solvent in which the fullerenes are soluble to dissolve the fullerenes in the solvent, and the soot residue insoluble in the solvent is removed therefrom to obtain the fullerene mixture.
Moreover, as a method for separation of a specific fullerene from the fullerene mixture, a separation method using a column filled with a separating agent such as activated carbon has been known. Another method has been known in which a host compound such as a calixarene or a cyclic phenol sulfide (a calixarene having a sulfur atom) is brought into contact with a specific fullerene (a guest compound) to form an inclusion compound, thereby separating the specific fullerene from fullerenes not included in the inclusion compound (See Japanese Patent No. 2654918 and Published Japanese Patent Application No. 11-240705, for example).